It started as a joke between friends, but Morris the cat's bid to become mayor of the Mexican city of Xalapa, the capital of the state of Veracruz, has now turned into a social media phenomenon with a serious message about political disenchantment.

"Morris has become an expression of how fed up people are with all the parties and a political system that does not represent us," said Sergio Chamorro, the owner of the furry black-and-white candidate whose first campaign slogan was: "Tired of voting for rats? Vote for a cat."

The Facebook page for the Candigato (gato means cat in Spanish) now has more than 130,000 "likes" – far more than those accrued by any of the candidates registered to stand in the Xalapa election, and more too than those of Veracruz's current governor. Mexico will hold local elections in around half of the country on 7 July.

Morris's Facebook page and website are filled with artwork, videos and slogans sent in by supporters from all over Mexico and beyond. Spin-off Twitter accounts have sprouted too, beyond the control of Chamorro and the small group of thirtysomething professionals who have run Morris's campaign since his popularity took off earlier this month.

A Morris campaign T-shirt. Photograph: Reuters

"The truth is that Morris no longer belongs to us. He belongs to his fans," said Chamorro, adding that he had even received messages from citizens designated to run the polling stations on election day describing their plans to ensure the cat's votes are registered and made public, even if they do not officially count.

Morris has also inspired a number of other animal candidates in other Mexican cities including a donkey in Ciudad Juárez, a dog in Oaxaca and a chicken in Tepic. None, however, have become as popular as the cat, which appears to have politicians and the authorities genuinely worried.

The head of Veracruz's electoral institute, which organises elections in the state, has urged members of the public not to waste their votes by spoiling their ballots with support for Morris. "It is important to vote for the registered candidates," Carolina Viveros said. "Please."

The cat's popularity also prompted the well-known columnist Julio Hernández to claim its candidacy was a front for the incumbent Institutional Revolutionary party's efforts to draw votes away from genuine electoral alternatives. Morris's team insist their point is precisely that they don't care who wins.

And beyond the election? The current plan is to put the cat's future public role to a vote of his Facebook friends.